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of this water in passing through the condenser must be multiplied
by the number of Ibs. per m. to find the total heat used.
(3). Heat left in condensed steam.—If all the heat calculations
were made from the temperature of the hot well, there would be
no need to state this result, but, as we are measuring from
32° datum, the heat left will be
Ibs. of steam per m. x (temp, condensed steam — 32)
Note that, if the engine is non-condensing, a hot well or tank
must be supplied, though not a condenser proper and air pump.
(4). Radiation and unaccounted is found by subtraction in
(5). Heat left in jacket water. — The jackets are drained regu-
larly, and the weight of water obtained. Multiply this by the
degrees of temperature above 32° to find the heat lost.
(6). Heat converted into work in cylinder.—This is the most
important statement, and must be arrived at with great care.
Indicator cards are taken every 10 minutes, and the I.H.P.
calculated from the usual formula (p. 625). Then
foot Ibs. per m.
B.T.U. per rn.
The revolutions may be taken by counter or speedometer, or
All the time the experiments are proceeding we are measuring
brake H.P. by absorption (p. 576 and 875) and are thus supplied
with data for mechanical efficiency (p. 770). Finally, the results
may be tabulated as follows:
(.) Thennal efficiency
(£) Efficiency of a perfect engine within same limits (see
p. 769, where r, = temp, live steam, and r2 = temp.
* hot well)
(c) Relative efficiency or comparison ratio (pp. 772 and 883)
(d] Mechanical efficiency.
The weight of dry steam per I.H.F. and per B.H.P. per hour
should also be given, and indeed are usually the only results
stated for commercial purposes. A graphic statement of the
data, as in Fig. 890, conduces to clearness.